In 1810 he advanced his controversy by explaining the nature of chlorine. Discovered long before by the indefatigable Scheele, it bore at the beginning of the nineteenth century the name oxymuriatic acid. Davy proved that it contained neither oxygen nor muriatic (hydrochloric) acid (though, as we know, it forms, with hydrogen, muriatic acid). He gave the name _chlorine_ because of the color of the gas (Greek, pale green). Davy studied later the compounds of fluorine, and though unable to isolate the element, conjectured its likeness to chlorine.
He lectured before the Dublin Society in 1810, and again in the following year; on the occasion of his second visit receiving the degree of LL.D. from Trinity College. He was knighted in the spring of 1812, and was married to a handsome, intellectual, and wealthy lady. He was appointed Honorary Professor of Chemistry at the Royal Institution. His new independence gave him full liberty to pursue his scientific interests. Toward the close of 1812 he writes to Lady Davy:--
"Yesterday I began some new experiments to which a very interesting discovery and a slight accident put an end. I made use of a compound more powerful than gunpowder destined perhaps at some time to change the nature of war and influence the state of society. An explosion took place which has done me no other harm than that of preventing me from working this day and the effects of which will be gone to-morrow and which I should not mention at all, except that you may hear some foolish exaggerated account of it, for it really is not worth mentioning...." The compound on the investigation of which he was then engaged is now known as the trichloride of nitrogen.
In the autumn of 1813 Sir Humphry and Lady Davy, accompanied by Michael Faraday, who on Davy's recommendation had in the spring of the same year received a post at the Royal Institution, set out, in spite of the continuance of the war, on a Continental tour. At Paris Sir Humphry was welcomed by the French scientists with every mark of distinction. A substance which had been found in the ashes of seaweed two years previously, by a soap-boiler and manufacturer of saltpeter, was submitted to Davy for chemical examination. Until Davy's arrival in Paris little had been done to determine its real character. On December 6 Gay-Lussac presented a brief report on the new substance, which he named _iode_ and considered analogous to chlorine. Davy, working with almost incredible rapidity in the presence of his rivals, was able a week later to sketch the chief characters of this new element, now known by the name he chose for it--_iodine_.